GuiTextBox(): Do not get previous code point when at start of string (#420)

Co-authored-by: segcore <[email protected]>

src/raygui.h

@@ -2611,16 +2611,17 @@ int GuiTextBox(Rectangle bounds, char *text, int textSize, bool editMode)
                 if (IsKeyPressed(KEY_BACKSPACE) || (autoCursorDelayCounter%RAYGUI_TEXTBOX_AUTO_CURSOR_DELAY) == 0)      // Delay every movement some frames
                 {
                     int prevCodepointSize = 0;
-                    GetCodepointPrevious(text + textBoxCursorIndex, &prevCodepointSize);
-
-                    // Move backward text from cursor position
-                    for (int i = (textBoxCursorIndex - prevCodepointSize); i < textLength; i++) text[i] = text[i + prevCodepointSize];
-
-                    // TODO Check: >= cursor+codepointsize and <= length-codepointsize
 
                     // Prevent cursor index from decrementing past 0
                     if (textBoxCursorIndex > 0)
                     {
+                        GetCodepointPrevious(text + textBoxCursorIndex, &prevCodepointSize);
+
+                        // Move backward text from cursor position
+                        for (int i = (textBoxCursorIndex - prevCodepointSize); i < textLength; i++) text[i] = text[i + prevCodepointSize];
+
+                        // TODO Check: >= cursor+codepointsize and <= length-codepointsize
+
                         textBoxCursorIndex -= codepointSize;
                         textLength -= codepointSize;
                     }
@@ -2638,7 +2639,7 @@ int GuiTextBox(Rectangle bounds, char *text, int textSize, bool editMode)
                 if (IsKeyPressed(KEY_LEFT) || (autoCursorDelayCounter%RAYGUI_TEXTBOX_AUTO_CURSOR_DELAY) == 0)      // Delay every movement some frames
                 {
                     int prevCodepointSize = 0;
-                    GetCodepointPrevious(text + textBoxCursorIndex, &prevCodepointSize);
+                    if (textBoxCursorIndex > 0) GetCodepointPrevious(text + textBoxCursorIndex, &prevCodepointSize);
 
                     if (textBoxCursorIndex >= prevCodepointSize) textBoxCursorIndex -= prevCodepointSize;
                 }